Biochemical characterization and cellular localization of 11S type storage proteins in olive (Olea europaea L.) seeds

Comprehensive Review on Fruit Seeds: Nutritional, Phytochemical, Nanotechnology, Toxicity, Food Biochemistry, and Biotechnology Perspective

Fruit seeds are leftovers from a variety of culinary sectors. They are generally unutilized and contribute greatly to global disposals. These seeds not only possess various nutritional attributes but also have many heath-beneficial properties. One way to make use of these seeds is to extract their bioactive components and create fortified food items. Nowadays, researchers are highly interested in creating innovative functional meals and food components from these unconventional resources. The main objective of this manuscript was to determine the usefulness of seed powder from 70 highly consumed fruits, including Apple, Apricot, Avocado, Banana, Blackberry, Blackcurrant, Blueberry, Cherry, Common plum, Cranberry, Gooseberry, Jackfruit, Jamun, Kiwi, Lemon, Mahua, Mango, Melon, Olive, Orange, and many more have been presented. The nutritional attributes, phytochemical composition, health advantages, nanotechnology applications, and toxicity of these fruit seeds have been fully depicted. This study also goes into in-depth detailing on creating useful food items out of these seeds, such as bakery goods, milk products, cereal-based goods, and meat products. It also identifies enzymes purified from these seeds along with their biochemical applications and any research openings in this area.

Exploitation of Olive (Olea europaea L.) Seed Proteins as Upgraded Source of Bioactive Peptides with Multifunctional Properties: Focus on Antioxidant and Dipeptidyl-Dipeptidase—IV Inhibitory Activities, and Glucagon-like Peptide 1 Improved Modulation

Agri-food industry wastes and by-products include highly valuable components that can upgraded, providing low-cost bioactives or used as an alternative protein source. In this context, by-products from olive production and olive oil extraction process, i.e., seeds, can be fostered. In particular, this work was aimed at extracting and characterizing proteins for Olea europaea L. seeds and at producing two protein hydrolysates using alcalase and papain, respectively. Peptidomic analysis were performed, allowing to determine both medium- and short-sized peptides and to identify their potential biological activities. Moreover, an extensive characterization of the antioxidant properties of Olea europaea L. seed hydrolysates was carried out both in vitro by 2,2-diphenyl-1-picrylhydrazyl (DPPH), by ferric reducing antioxidant power (FRAP), and by 2,2′-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) assays, respectively, and at cellular level by measuring the ability of these hydrolysates to significant reduce the H₂O₂-induced reactive oxygen species (ROS) and lipid peroxidation levels in human intestinal Caco-2 cells. The results of the both hydrolysates showed significant antioxidant properties by reducing the free radical scavenging activities up to 65.0 ± 0.1% for the sample hydrolyzed with alcalase and up to 75.7 ± 0.4% for the papain hydrolysates tested at 5 mg/mL, respectively. Moreover, similar values were obtained by the ABTS assays, whereas the FRAP increased up to 13,025.0 ± 241.5% for the alcalase hydrolysates and up to 12,462.5 ± 311.9% for the papain hydrolysates, both tested at 1 mg/mL. According to the in vitro results, both papain and alcalase hydrolysates restore the cellular ROS levels up 130.4 ± 4.24% and 128.5 ± 3.60%, respectively, at 0.1 mg/mL and reduce the lipid peroxidation levels up to 109.2 ± 7.95% and 73.0 ± 7.64%, respectively, at 1.0 mg/mL. In addition, results underlined that the same hydrolysates reduced the activity of dipeptidyl peptidase-IV (DPP-IV) in vitro and at cellular levels up to 42.9 ± 6.5% and 38.7 ± 7.2% at 5.0 mg/mL for alcalase and papain hydrolysates, respectively. Interestingly, they stimulate the release and stability of glucagon-like peptide 1 (GLP-1) hormone through an increase of its levels up to 660.7 ± 21.9 pM and 613.4 ± 39.1 pM for alcalase and papain hydrolysates, respectively. Based on these results, olive seed hydrolysates may represent new ingredients with antioxidant and anti-diabetic properties for the development of nutraceuticals and functional foods for the prevention of metabolic syndrome onset.

Characterisation of Endogenous Peptides Present in Virgin Olive Oil

The low molecular weight peptide composition of virgin olive oil (VOO) is mostly unknown. We aimed to investigate the composition of the endogenous peptides present in VOO, the protein sources from which those peptides originate and their biological activities. A water-soluble extract containing peptides was obtained from VOO. The peptides were separated by size-exclusion using fast protein liquid chromatography, and the low molecular weight fraction (1600–700 kDa) was analysed by nanoscale liquid chromatography Orbitrap coupled with tandem mass spectrometry and de novo sequencing. Nineteen new peptides were identified by Peaks database algorithm, using the available Olea europaea (cv. Farga) genome database. Eight new peptides were also identified by Peaks de novo sequencing. The protein sources of the peptides detected in the database by Peaks DB were identified by BLAST-P search. Seed storage proteins were among the most frequent sources of VOO peptides. BIOPEP software was used to predict the biological activities of peptides and to simulate (in silico) the proteolytic activity of digestive enzymes on the detected peptide sequences. A selection of synthetic peptides was obtained for investigation of their bioactivities. Peptides VCGEAFGKA, NALLCSNS, CPANGFY, CCYSVY and DCHYFL possessed strong ACE-inhibitory and antioxidant activities in vitro. Antioxidant peptides could play a role in VOO quality.

Identification of seed storage proteins as the major constituents of the extra virgin olive oil proteome

Proteins are minor components of extra virgin olive oil (EVOO), but the nature of the olive oil proteome is still elusive. In this paper, we have uncovered the EVOO proteome for the first time. Seed storage proteins of globulin-type were identified as the most abundant proteins in EVOO, which also contains an active 13-lipoxygenase and several potential allergenic proteins, including the "panallergen" profilin. We validated our proteomic data by Western blotting and enzyme activity assays. Our data also demonstrated that the seed is the main source of proteins in EVOO, while the contribution of the pulp is uncertain and needs further verification. The impact of EVOO proteins on its stability and quality, and on human health is discussed.

Nutritional profile and nutraceutical components of olive (Olea europaea L.) seeds

Olive seeds, a potential food by-product from both table olive and olive oil industries, were examined for their overall proximate composition, oil, protein, mineral and phenolic components. Proximate analysis indicates that olive seeds are an unusually rich source of total dietary fibre (≅ 47% dry weight basis, DWB), as well as lipids (≅ 30%) and proteins (≅ 17%). Oil composition shows high levels of oleic (≅ 62% of total fatty acids) and linoleic (≅ 24%) acids, moderate concentrations of tocopherols (≅ 460 mg/kg) and squalene (≅ 194 mg/kg), and relatively high amounts of several sterols and non-steroidal triterpenoids. Olive seed proteins are a rich source of essential amino acids (about 46% of the total AA content). Olive seeds also contain significant amounts of some essential macro-elements (K, Ca, Mg, Na, P) and micro-elements (Zn, Mn, Cu). Phenolic compounds are present at relatively high quantities (≅ 2.8 mg/g seed, DWB); the most abundant belong to the group of secoiridoid compounds (elenolic acid derivatives) including oleuropein and structurally related substances (demethyloleuropein and ligstroside), and nüzhenide derivatives. Based on the general nutritional profile and nutraceutical components, olive seeds have value-added potential as a source of edible oil, proteins or meal serving as feed supplements.

Implications of denitrification in the ecological status of an urban river using enzymatic activities in sediments as an indicator

A better understanding of the effects of a number of environmental factors on denitrification is vital for analyzing its role as nitrogen sink and providing deeper knowledge about the ecological status of a nitrate-rich ecosystem. Since few studies have addressed the occurrence and implications of denitrification in river sediments, and complexity of interactions among all these environmental factors makes comprehension of the process difficult, the potential of sediments from the Deba River to attenuate nitrate excess through denitrification was investigated. For this purpose, we adapted an in vitro method to measure activities of two enzymes contributing to the entire multiple-step nitrate reduction: Nitrate Reductase and Nitrite Reductase. The environmental features that influence both or single enzymatic activities were identified as oxygen availability, regulated directly by the moisture content or indirectly through the aerobic respiration, organic matter and nitrate content of sediments, and electrical conductivity and exchangeable sodium percentage of water. Additionally, our results showed that Nitrate Reductase catalyzes the principal limiting step of denitrification in sediments. Therefore, taking this enzymatic activity as an indicator, the southern part of the Deba River catchment presented low potential to denitrify but nitrate-limited sediments, whereas the middle and northern parts were characterized by high denitrification potential but nitrate-rich sediments. In general, this study on denitrifying enzymatic activities in sediments evaluates the suitability of the management of the effluents from wastewater treatment plants and municipal sewages to ensure a good ecological status of the Deba River.

Histological Features of the Olive Seed and Presence of 7S-Type Seed Storage Proteins as Hallmarks of the Olive Fruit Development

The production of olive oil is an important economic engine in the Mediterranean area. Nowadays, olive oil is obtained mainly by mechanical processes, by using the whole fruit as the primary raw material. Although the mesocarp is the main source of lipids contributing to olive oil formation, the seed also contributes to the olive oil composition and attributes. The olive seed is also becoming an interesting emerging material itself when obtained after alternative processing of the olive fruit. Such seed is used for the production of differential oil and a unique flour among other bioactive products, with increasing uses and applications in cosmetics, nutrition, and health. However, olive seed histology has been poorly studied to date. A complete description of its anatomy is described for the first time in the present study by using the 'Picual' cultivar as a model to study the development of the different tissues of the olive seed from 60 to 210 days after anthesis. A deep analysis of the seed coats, endosperm storage tissue and the embryo during their development has been performed. Moreover, a panel of other olive cultivars has been used to compare the weight contribution of the different tissues to the seed, seed weight variability and the number of seeds per fruit. In addition to the histological features, accumulation of seed storage proteins of the 7S-type (β-conglutins) in the seed tissues has been assessed by both biochemical and immunocytochemical methods. These hallmarks will help to settle the basis for future studies related to the location of different metabolites along the olive seed and mesocarp development, and therefore helping to assess the appropriate ripening stage for different commercial and industrial purposes.

Biogenesis of protein bodies during legumin accumulation in developing olive (Olea europaea L.) seed

Much of our current knowledge about seed development and differentiation regarding reserves synthesis and accumulation come from monocot (cereals) plants. Studies in dicotyledonous seeds differentiation are limited to a few species and in oleaginous species are even scarcer despite their agronomic and economic importance. We examined the changes accompanying the differentiation of olive endosperm and cotyledon with a focus on protein bodies (PBs) biogenesis during legumin protein synthesis and accumulation, with the aim of getting insights and a better understanding of the PBs' formation process. Cotyledon and endosperm undergo differentiation during seed development, where an asynchronous time-course of protein synthesis, accumulation, and differential PB formation patterns was found in both tissues. At the end of seed maturation, a broad population of PBs, particularly in cotyledon cells, was distinguishable in terms of number per cell and morphometric and cytochemical features. Olive seed development is a tissue-dependent process characterized by differential rates of legumin accumulation and PB formation in the main tissues integrating seed. One of the main features of the impressive differentiation process is the specific formation of a broad group of PBs, particularly in cotyledon cells, which might depend on selective accumulation and packaging of proteins and specific polypeptides into PBs. The nature and availability of the major components detected in the PBs of olive seed are key parameters in order to consider the potential use of this material as a suitable source of carbon and nitrogen for animal or even human use.

Identification and Assessment of the Potential Allergenicity of 7S Vicilins in Olive (Olea europaea L.) Seeds

Olive seeds, which are a raw material of interest, have been reported to contain 11S seed storage proteins (SSPs). However, the presence of SSPs such as 7S vicilins has not been studied. In this study, following a search in the olive seed transcriptome, 58 sequences corresponding to 7S vicilins were retrieved. A partial sequence was amplified by PCR from olive seed cDNA and subjected to phylogenetic analysis with other sequences. Structural analysis showed that olive 7S vicilin contains 9 α-helixes and 22 β-sheets. Additionally, 3D structural analysis displayed good superimposition with vicilin models generated from Pistacia and Sesamum. In order to assess potential allergenicity, T and B epitopes present in these proteins were identified by bioinformatic approaches. Different motifs were observed among the species, as well as some species-specific motifs. Finally, expression analysis of vicilins was carried out in protein extracts obtained from seeds of different species, including the olive. Noticeable bands were observed for all species in the 15-75 kDa MW interval, which were compatible with vicilins. The reactivity of the extracts to sera from patients allergic to nuts was also analysed. The findings with regard to the potential use of olive seed as food are discussed.

Proteins in olive fruit and oil

This paper is a comprehensive review grouping the information on the extraction, characterization, and quantitation of olive and olive oil proteins and providing a practical guide about these proteins. Most characterized olive proteins are located in the fruit, mainly in the seed, where different oleosins and storage proteins have been found. Unlike the seed, the olive pulp contains a lower protein content having been described a polypeptide of 4.6 kDa and a thaumain-like protein. Other important proteins studied in olive fruits have been enzymes which could play important roles in olives characteristics. Part of these proteins is transferred from the fruit to the oil during the manufacturing process of olive oil. In fact, the same polypeptide of 4.6 kDa found in the pulp has been described in the olive oil and, additionally, the presence of other proteins and enzymes have also been described. Protein profiles have recently been proposed as an interesting strategy for the varietal classification of olive fruits and oils. Nevertheless, there is still a lot of knowledge without being explored requiring new studies focused on the determination and characterization of these proteins.

Olive seed protein bodies store degrading enzymes involved in mobilization of oil bodies

The major seed storage reserves in oilseeds are accumulated in protein bodies and oil bodies, and serve as an energy, carbon, and nitrogen source during germination. Here, the spatio-temporal relationships between protein bodies and several key enzymes (phospholipase A, lipase, and lipoxygenase) involved in storage lipid mobilization in cotyledon cells was analysed during in vitro seed germination. Enzyme activities were assayed in-gel and their cellular localization were determined using microscopy techniques. At seed maturity, phospholipase A and triacylglycerol lipase activities were found exclusively in protein bodies. However, after seed imbibition, these activities were shifted to the cytoplasm and the surface of the oil bodies. The activity of neutral lipases was detected by using α-naphthyl palmitate and it was associated mainly with protein bodies during the whole course of germination. This pattern of distribution was highly similar to the localization of neutral lipids, which progressively appeared in protein bodies. Lipoxygenase activity was found in both the protein bodies and on the surface of the oil bodies during the initial phase of seed germination. The association of lipoxygenase with oil bodies was temporally correlated with the appearance of phospholipase A and lipase activities on the surface of oil bodies. It is concluded that protein bodies not only serve as simple storage structures, but are also dynamic and multifunctional organelles directly involved in storage lipid mobilization during olive seed germination.

Analytical approaches for the characterization and identification of olive (Olea europaea) oil proteins

Proteins in olive oil have been scarcely investigated probably due to the difficulty of working with such a lipidic matrix and the dramatically low abundance of proteins in this biological material. Additionally, this scarce information has generated contradictory results, thus requiring further investigations. This work treats this subject from a comprehensive point of view and proposes the use of different analytical approaches to delve into the characterization and identification of proteins in olive oil. Different extraction methodologies, including capture via combinational hexapeptide ligand libraries (CPLLs), were tried. A sequence of methodologies, starting with off-gel isoelectric focusing (IEF) followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) or high-performance liquid chromatography (HPLC) using an ultraperformance liquid chromatography (UPLC) column, was applied to profile proteins from olive seed, pulp, and oil. Besides this, and for the first time, a tentative identification of oil proteins by mass spectrometry has been attempted.

Identification of olive (Olea europaea) seed and pulp proteins by nLC-MS/MS via combinatorial peptide ligand libraries

Different types of extraction protocols are described for identifying proteins in seed and pulp of olive (Olea europea), by employing both conventional extraction methods and capture with ProteoMiner as well as with in house-made combinatorial peptide ligand libraries (HM-CPLLs) at pH 7.4 and at pH 2.2. Thanks to the use of CPLLs, able to dramatically amplify the signal of low-abundance species, a quite large number of compounds has been indeed identified: 61 in the seed (vs. only four reported in current literature) and 231 in the pulp (vs. 56 described so far), the deepest investigation up to the present of the olive proteome. In the seed, it highlights the presence of seed storage proteins, oleosins and histones. In the pulp, the allergenic thaumatin-like protein (Ole e 13) was confirmed, among the other 231, as the most abundant protein in the olive pulp. The present research has also been undertaken with the aim of identifying proteins in olive oil and ascertaining the relative contribution of seed and pulp proteins in their presence, if any, in oils.

Development of the cotyledon cells during olive (Olea europaea L.) in vitro seed germination and seedling growth

The structural changes occurred in differentiating olive cotyledon cells into mesophyll cells are described. Using histological and immunocytological methods as well as microscopic observations, we showed that in the cells of mature embryo, large electron-dense proteins bodies (PBs) are surrounded by numerous oil bodies (OBs). After 3 days of in vitro germination, the presence of large PBs originated by fusion of smaller PBs was observed. It was also detected a close spatial proximity between PBs and OBs, likely as a reflection of interconnected metabolic pathways. Between the 3rd and the 12th day of germination, the formation of a large vacuolar compartment takes place accompanied by a decrease in the PBs and OBs number. This was coincident with a progressive decrease in the amount of the 11S-type seed storage proteins (SSPs), showed in situ and after Western blot analysis of crude protein extracts. After 26 days germination, the cellular organization became typical for a leaf mesophyll cell, with well-differentiated chloroplasts surrounding a large central vacuole. Our results suggest that the olive cotyledon storage reserves are mobilized gradually until the seedling becomes autotrophic. Moreover, the specific accumulation of storage proteins in the intravacuolar material suggests that these structures may operate as a shuttle for SSPs and/or products of their degradation into the cytoplasm, where finally they supply amino acids for the differentiating mesophyll cells.

Characterization of a caleosin expressed during olive (Olea europaea L.) pollen ontogeny

BACKGROUND

The olive tree is an oil-storing species, with pollen being the second most active site in storage lipid biosynthesis. Caleosins are proteins involved in storage lipid mobilization during seed germination. Despite the existence of different lipidic structures in the anther, there are no data regarding the presence of caleosins in this organ to date. The purpose of the present work was to characterize a caleosin expressed in the olive anther over different key stages of pollen ontogeny, as a first approach to unravel its biological function in reproduction.

RESULTS

A 30 kDa caleosin was identified in the anther tissues by Western blot analysis. Using fluorescence and transmission electron microscopic immunolocalization methods, the protein was first localized in the tapetal cells at the free microspore stage. Caleosins were released to the anther locule and further deposited onto the sculptures of the pollen exine. As anthers developed, tapetal cells showed the presence of structures constituted by caleosin-containing lipid droplets closely packed and enclosed by ER-derived cisternae and vesicles. After tapetal cells lost their integrity, the caleosin-containing remnants of the tapetum filled the cavities of the mature pollen exine, forming the pollen coat. In developing microspores, this caleosin was initially detected on the exine sculptures. During pollen maturation, caleosin levels progressively increased in the vegetative cell, concurrently with the number of oil bodies. The olive pollen caleosin was able to bind calcium in vitro. Moreover, PEGylation experiments supported the structural conformation model suggested for caleosins from seed oil bodies.

CONCLUSIONS

In the olive anther, a caleosin is expressed in both the tapetal and germ line cells, with its synthesis independently regulated. The pollen oil body-associated caleosin is synthesized by the vegetative cell, whereas the protein located on the pollen exine and its coating has a sporophytic origin. The biological significance of the caleosin in the reproductive process in species possessing lipid-storing pollen might depend on its subcellular emplacement. The pollen inner caleosin may be involved in OB biogenesis during pollen maturation. The protein located on the outside might rather play a function in pollen-stigma interaction during pollen hydration and germination.

First ultraperformance liquid chromatography based strategy for profiling intact proteins in complex matrices: application to the evaluation of the performance of olive ( Olea europaea L.) stone proteins for cultivar fingerprinting

There is a clear need for accelerating protein separations by HPLC. Different proposals have been developed including the use of perfusion and monolithic stationary phases. Nevertheless, these stationary phases, in some occasions, do not provide enough efficiency to resolve these large molecules when they are present in complex matrices. Although ultraperformance liquid chromatography (UPLC) columns have been successfully used for the efficient and rapid separation of small molecules, this is the first time these columns were proposed for the separation of intact proteins in a real complex matrix: the olive stone. Two different strategies were employed for the extraction of olive proteins: enzymatic assisted extraction and buffered extraction. Five different columns traditionally employed for the separation of proteins were used, and results were compared with those obtained when using different sub-2 microm particle columns. Separations obtained with sub-2 mum particle columns significantly improved the separations obtained with the other columns. This paper also demonstrates the applicability of protein profiles obtained from the olive stone for the discrimination among olive varieties.

Identification and localization of a caleosin in olive (Olea europaea L.) pollen during in vitro germination

In plant organs and tissues, the neutral storage lipids are confined to discrete spherical organelles called oil bodies. Oil bodies from plant seeds contain 0.6-3% proteins, including oleosins, steroleosins, and caleosins. In this study, a caleosin isoform of approximately 30 kDa was identified in the olive pollen grain. The protein was mainly located at the boundaries of the oil bodies in the cytoplasm of the pollen grain and the pollen tube. In addition, caleosins were also visualized in the cytoplasm at the subapical zone, as well as in the tonoplast of vacuoles present in the pollen tube cytoplasm. The cellular behaviour of lipid bodies in the olive pollen was also monitored during in vitro germination. The number of oil bodies decreased 20-fold in the pollen grain during germination, whereas the opposite tendency occurred in the pollen tube, suggesting that oil bodies moved from one to the other. The data suggest that this pollen caleosin might have a role in the mobilization of oil bodies as well as in the reorganization of membrane compartments during pollen in vitro germination.

Comparative proteomical analysis of zygotic embryo and endosperm from Coffea arabica seeds

During coffee seed development, proteins are predominantly deposited in cotyledons and in the endosperm. Reserve proteins of the 11S family are the most abundant globulins in coffee seeds, acting as a nitrogen source during roasting and guaranteeing flavor and aroma. The aim of the present study was to compare the protein profiles of endosperm and zygotic embryos of coffee seeds. Proteins were extracted from whole seed as well as from embryo and endosperm, separately. Total proteins were analyzed by two-dimensional electrophoresis (2-DE) followed by identification by mass spectrometry (MS). The most abundant spots observed in the gels of coffee seeds were excised, digested with trypsin, and identified by MS as subunits of the 11S globulin. Spots with identical pI and molecular masses were also observed in the protein profiles of coffee endosperm and embryo, indicating that 11S protein is also highly expressed in those tissues. Peptide sequence coverage of about 20% of the entire 11S globulin was obtained. Three other proteins were identified in the embryo and endosperm 2-DE profiles as a Cupin superfamily protein, an allergenic protein (Pru ar 1), exclusive to the endosperm 2D map, and a hypothetical protein, observed only in the zygotic embryo profile.

Optimizing protein extraction from plant tissues for enhanced proteomics analysis

Plant tissues usually contain high levels of proteases and secondary metabolites that severely interfere with protein extraction, separation, and identification. Preparation of high-quality protein samples from plant tissues for proteomic analysis represents a great challenge. This article briefly describes the critical points in protein separation, especially secondary metabolites in plant tissues, and removal strategy. It provides an updated overview of three total protein extraction methods and their applications in proteomic analysis of various recalcitrant tissues.

Olive stone an attractive source of bioactive and valuable compounds

The olive stone and seed are an important byproduct generated in the olive oil extraction and pitted table olive industries. As a lignocellulosic material, the hemicellulose, cellulose and lignin are the main components of olive stone as wells as protein, fat, phenols, free sugars and poliols composition. The main use of this biomass is as combustion to produce electric energy or heat. Other uses such as activated carbon, furfural production, plastic filled, abrasive and cosmetic or other potential uses such as biosorbent, animal feed or resin formation have been cited. In this article, an overview of the characterization and main uses of olive stone and seed are described for the first time. Also, this review discusses the potential use of this material based on each component. In this way, a new approach to the olive stone and seed by pretreating with a steam explosion followed by chemical fractionation is described.